netdev - Re: [PATCH v3] filter: Optimize instruction revalidation code.

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Message-ID: <fb1f2f80c2a0663226799d4fa345d0f8@localhost>
Date:	Wed, 17 Nov 2010 10:01:56 +0100
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	<eric.dumazet@...il.com>, <mjt@....msk.ru>, <davem@...emloft.net>,
	<drosenberg@...curity.com>, <xiaosuo@...il.com>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH v3] filter: Optimize instruction revalidation code.

On Wed, 17 Nov 2010 17:06:10 +0900, Tetsuo Handawrote:

> If compilers can generate better code for continuous case values
> than discontinuous case values, then keeping BPF_S_* makes sense.

Yes, this is crucial. A compiler cannot generate a jump table of O(1) for
dense labels. The BPF_S_* translation was done to convert to a dense label
construct. So this "optimization" is a no-go.

Look at the log and read my comment for a detailed explanation.

Anyway: "code--" increments the _copied_ value, not the value in the
evaluated opcode itself. I will validate the patch!

Hagen
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